This study proposes to investigate the coordinate basis for visual processing of retinal slip information in the pretectum (PT) and accessory optic system (AOS) of the monkey. This will be done by finding the planes of visual surround motion that produce maximal excitation and inhibition in neurons in these regions. Alert rhesus and cynomolgus monkeys will be used. They will be trained to watch spots of light projected on a screen. Using a planetary projector, motion of the visual surround will be produced in various planes around axes going through the center of the head. Visual motion in other planes will also be used. PT and AOS units, recorded extracellularly, will be identified wherever possible by antidromic and orthodromic stimulation. They will be tested to determine which planes of visual surround motion produce the greatest and least response. We anticipate that the maximum and minimum response planes of many PT and AOS neurons will be parallel to the planes of the semicircular canals. Effects of changes in eye position will be tested to determine if a central representation of retinal slip in stimulus planes is represented in activity of PT and AOS neurons. At regions where unt activity is associated with motion in various spatial planes, we will electrically stimulate and determine the plane of the induced eye movements. Electrolytic and chemical lesions will be made in PT and AOS and effects on OKN and OKAN will be determined. The visual cortex will be lesioned and effects on the response of PT and AOS neurons to surround motion will be noted. Finally, the pathways by which activity reaches the vestibular nuclei from PT and AOS will be determined. When this work is completed, we should have a clearer idea of how retinal slip related to head motion is coded, and over what pathways it projects to the brainstem. We should also understand better the organization of the subcortical visual system that sends activity to the vestibular system to help stabilize gaze during head movements.